Composite material systems which combine two or more distinct component materials are of increasing importance to meet demands for materials possessing an array of desirable properties. Typical composite materials comprise a reinforcing material disposed in a matrix material to create a new material which combines the desirable properties of the components and/or has properties that may not be present, or present to the same extent, in the components alone.
A significant class of composite material comprises a material with plural two-dimensional plies of fibrous reinforcing material disposed in a suitable matrix material. The plies of fibrous reinforcing material effect reinforcement in one or two dimensions, for example in that they comprise long fibres which usually substantially span the length and/or breadth of the ply, and hence of the composite material. Suitable plies for such purposes include unidirectional tapes with parallel fibres and bidirectional sheets in which fibres are arrayed in plural directions, and may be non-woven sheets or have a woven, braided stitched or other like structure. Composite materials reinforced with relatively long fibres in this manner are usually referred to as continuous fibre reinforced composites (CFRCs) to distinguish them from short fibre reinforced.
An acknowledged inherent weakness of CFRCs reinforced with plural laminar plies of fibrous reinforcing material is interlaminar or out of plane weakness. The fibre reinforcement may bear most of the load in the plane of the fibres. As CFRCs lack fibre reinforcement out of this plane, they possess a lesser load bearing capability in this direction. As a result, CFRCs tend to exhibit relatively lower interlaminar strength and/or fracture toughness, and interlaminar failure, for example by delamination, may occur at undesirably low levels of applied stress.
To mitigate this, solutions have been offered that tie the plies together in some mechanical manner in the third dimension, for example by braiding or stitching plies together to give additional through thickness strength. Such solutions have met limited success. In particular, they can reduce in plane strength by affecting the integrity of the in plane fibre structure. Moreover, if the third dimension braiding or stitching is to be effective this tends to require the reinforcement plies themselves to have a woven or similarly integrated two dimensional architecture, whereas for many applications it might otherwise be desirable to use non-woven sheet materials or unidirectional tape.
Provision of an enhanced material structure and method of fabrication providing for reinforcement in a third, out of plane dimension in CRFCs, and in particular a structure and method that limits any detrimental effect on in plane reinforcement and/or that is applicable to reinforcement plies with a variety of fibre structures, for example including non-woven sheets and unidirectional tape as well as woven structures, is therefore desirable.